Clarke Xu

Development of a diamine biosensor

An amperometric diamine sensor is developed for clinical applications in diagnosis of bacterial vaginosis (BV). The sensor is based on crosslinked putrescine oxidase (PUO) which catalyzes the conversion of diamines (mainly putrescine and cadaverine) to products including hydrogen peroxide. The hydrogen peroxide is detected anodically at platinum electrode polarized at 0.5 V versus Ag/AgCl. Platinum-plated gold electrodes used as a substrate for the sensor construction, are batch-fabricated on a flexible polyimide foil (Kapton(R), DuPont). A three-electrode cell configuration is used in all amperometric measurements. The sensor construction is based on three layers: an inner layer to reject the interference effect of oxidizable molecules, an outer diffusion controlling layer, and in addition, an enzyme middle layer. The enzyme layer was immobilized by crosslinking PUO with bovine serum albumin (BSA) using glutaraldehyde (GA). An optimization study of the enzyme solution composition was carried out. With the optimized enzyme layer, the biosensor showed a very high sensitivity and fast response time of ca. 20 s. The sensor has a linear dynamic range from (0.5-300 muM) for putrescine that covers the expected biological levels of the analyte. Details on sensor fabrication and characterization are given in the present work.

Wet and dry chemistry kits for total creatine kinase activity using a microfabricated, planar, small-volume, amperometric cell

Abstract A novel microfabricated amperometric microcell is used for total creatine kinase (CK) activity determination. The microcell employs a photolithograpically prepared flat form electrode pair for detection. The enzyme-catalyzed reaction takes place in a thin liquid film, supported by a replaceable porous, hydrophillic membrane, resting on the working electrode surface. Simple, two electrode, amperometry was used, to avoid overvoltage shocks caused by “open” circuits. An electrochemically prepared size-exclusion membrane was utilized on the working electrode to provide selectivity for the amperometric detection of hydrogen peroxide. Two different analytical reaction sequences following the CK catalyzed creatine phosphate hydrolysis were investigated. Both result in hydrogen peroxide production. The rate of hydrogen peroxide production is proportional to the total CK activity, and it is followed after the dispensation of sample into the microcell. The slope of the amperometric current–time curve is evaluated as the analytical signal.